1. Field of the Invention
The present invention relates to a conductive composition, and an electrophotographic belt and an image forming apparatus using the conductive composition. The present invention also relates to a method of manufacturing the conductive composition.
2. Description of the Background
Endless belts are widely used as components of intermediate transfer devices, developing devices, or photoconductor devices in electrophotographic copiers and laser beam printers. For example, an electrophotographic image forming apparatus employs an endless belt as a transfer belt onto which a toner image is transferred. The transfer belt is required to have a stable electric resistivity, mechanical strength, and a long lifespan. To meet these requirements, thermosetting resins such as polyimide and polyamide-imide have been used for the transfer belt.
Polyimide and polyamide-imide are generally formed by subjecting a fluid varnish to processes of application, drying, and curing. Because the curing process takes a long time, polyimide and polyamide-imide cannot be continuously produced. Also, unit prices of polyimide and polyamide-imide are high. Polyimide and polyamide-imide containing conductive particles, such as carbon black, to have a certain electric resistivity, have high elasticity and are resistant to stretch. However, they need reinforcing tape on their ends because they are easily breakable, resulting in cost rise.
In view of this situation, there is an approach for using thermoplastic resins in place of thermosetting resins. Unlike thermosetting resins, thermoplastic resins can be continuously produced at low cost. But they are unstable in electric resistivity and unresistant to creep or stretch, which may result in a short life span.
In attempting to solve such problems, various conductive compositions have been proposed.
For example, Japanese Patent Application Publication No. (hereinafter JP-A) 2002-241562 proposes a conductive composition comprising a fluoropolymer, a conductive compound, and a tri-block copolymer. JP-04-022013-A proposes a composite body comprising a flexible conductive sheet covered with a conductive polymer.
However, neither of them has satisfactory manufacturability, electric property, and durability.
Japanese Patent No. 3738628 discloses a composition comprising a polyamide, a thermoplastic resin having a specific viscoelasticity, and a compatibilizing agent. However, the compatibilizing agent (e.g., vinyl graft polymer, acrylonitrile-styrene copolymer, maleic anhydride) does not satisfactorily improve resistant to creep or crack. There is no mention of stabilization of electric resistivity.
Japanese Patent Application Publication No. 2002-304065 proposes an electrophotographic belt comprising a fluorine-based binder and an epoxy-resin-covered carbon black, to which an additive having an amine value of 5 to 120 is adhered. But this composition has poor strength and stiffness.